Hotels after security Schipol

Sorry I can't help with this. What time is your flight? Maybe you should reach out to KLM directly to find out if they will let you check your bag the night before, and if there is a window time to do so.
If you cannot, as you probably already know, there are 3 hotels connected to the airport on landside (before security). I'm actually going to stay at one of them later this summer, as I have a 8am flight next day back to US.

You will have to check with KLM. According to the interwebs you might be able check bags the day ahead, but other sources say you can only check bags the day of your flight. Schiphol has self service bag check so you don't need a staffed desk, but you want to be really sure of the timing. As noted there are three hotels landside of the airport that are extremely short walk to the terminal (Citizen M, Hilton, Sheraton).

+1 800 618 0104 8AM to 11PM ( Eastern)
https://www.klm.com/contact/topic/booking/subtopic/book-flight-option

Thank you for your responses everyone. Our flight is at 7:20 and I was hoping not to have to deal with checking a bag and going through security that early in the morning hence the idea of staying at the Mercure which is after security. What I ended up doing was just looking to see what the latest flight out of Amsterdam was to Rome and then one would have to assume that the bag desk would be open until at least an hour before that flight which is at 9:05 p.m. so I would imagine if we got to the airport by 7:00 we would be fine. The other answer that I will need to get is if they allow you to check a bag that early for a flight in the morning.

And checking further it looks like they don't "officially" offer "Twilight baggage drop off" at at Schiphol so I guess I'll have to suck it up and get there around 5:30 to get the bag checked.

Use the Schiphol Airport planner and plug in your specific flight - it will tell you exactly what time the airport thinks you should arrive, where your check in desks are located, how busy security will be, etc. You can start checking about two weeks ahead of your flight but some of the details won't fill in until a couple days ahead. https://www.schiphol.nl/en/departures/ The airport also has an app that shows the same info.

Mala2025 - Maybe you should still spend last evening at the airport, just landside. I found best rate at Hilton vs Sheraton vs CitizenM for my trip. But check them for your date.
That way you are only 10 min walk to checkin area/security. And you can monitor how busy it might be using the link shared above.

What we have decided to do is spend our 5 nights in Delft (which is close enough to everything yet SO much cheaper and more relaxed...and it's CUTE). We'll do a bunch of day trips to Amsterdam and surrounding areas by train. There is a direct train to AMS (35-45 min.) many times a day from Delft so we will do that versus staying at the airport.